In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 by Brownstein entitled "Apparatus and Method For Controlling A Thermal Printer Apparatus," issued Nov. 4, 1986, the disclosure of which is hereby incorporated by reference.
Thermal dye transfer as described above is a well-established procedure for production of an image in a polymeric receiver sheet. There are certain physical requirements, some quite severe, relative to thickness, flatness, flexibility, and shape of such receivers when used in thermal head, laser, flash, or other thermal printing devices. Such restrictions limit the applicability of thermal dye transfer to non-planar objects. It would be desirable to have a process whereby an image generated by a thermal printing device could be formed on an object with few, if any, restrictions of thickness, flatness, shape and flexibility.
Japanese Kokais 62-66997 (Nitto Electric Ind. Co. LTD) and 60-203494 (Ricoh K.K.) disclose forming images in a transparent receiver by thermal dye transfer and then adhering the receiver to an object/mount. This makes possible forming thermal dye transfer images on a wider variety of objects than direct thermal dye transfer to the object, but the presence of an adhered receiver is objectionable in that it results in a raised surface appearance.
EP 0 266 430 (Dai Nippon Insatsu K. K.) discloses a process for formation of a dye transfer image on an arbitrary object comprising forming an image in a dye-receiving layer of a transferrable sheet, separating the dye image-receiving layer from its support, and adhering the dye image-receiving layer to the arbitrary object. By separating the image-receiving layer from its support, a thinner receiver is adhered to the object. While this approach may reduce objections to a raised surface appearance due to the adhered layer, there is still the problem of adhering the image containing layer permanently to the object.
Co-pending, commonly assigned U.S. Ser. No. 07/519,603 referred to above of Kaszczuk and Mruk, the disclosure of which is hereby incorporated by reference, discloses a process whereby a thermal dye transfer image can be formed on an object of arbitrary shape without having to permanently adhere a separate layer to such objects. This process requires use of an intermediate dye-receiving element comprising a support and a seperable dye image-receiving layer. After an image is formed in the dye image-receiving layer by conventional means, the imaged intermediate receiving layer is separated from the support and placed in contact with an arbitrarily shaped final receiver. The dye image is then retransferred out of the intermediate receiving layer and into the final receiver by the action of heat.
A preferred intermediate receiving element disclosed in Ser. No. 07/519,603 comprises a paper support, an unsubbed polyolefin layer extrusion coated on the paper support, and a dye image-receiving layer coated on the polyolefin layer. The polyolefin layer's moderate adhesion to the support allows for support removal from the remaining layers of the intermediate receiving element, and the polyolefin layer also provides adequate strength and dimensional stability for the remaining layers during the dye retransfer step to the final receiver.
When a paper stock overcoated with a polyolefin layer is used as the support for an intermediate receiver as described above, it is important that a strong bond be established between the polyolefin layer and the adjacent dye-receiving layer. If this bond is weak, the dye image-receiving layer may separate from the polyolefin layer itself when the paper support is to be stripped at the polyolefin interface and it may not be possible to have an integral sheet of sufficient cohesiveness suitable for retransfer. There is thus a need for a strong bonding subbing layer at the polyolefin interface.
Subbing layers of the prior art are not satisfactory for this purpose. Polyvinylidene chloride derived materials have been used as dye receiver subbing layers (U.S. Pat. No. 4,748,150) but form too weak a bond for the present use. Metal alkoxide (such as titanium tetra-n-butoxide) and alkoxysilane derived polymers are generally more effective subbing layers, but these materials are subject to hydrolysis and are thus difficult to coat in a reproducible manner.
It would be desirable to provide an intermediate dye-receiving element which would have sufficient adhesion between a polymeric dye image-receiving layer and a polyolefin layer coated on a support such that the support could be removed from the polyolefin and dye image-receiving layers while retaining the polyolefin and dye image-receiving layers together as a cohesive unit.